1. Field of the Invention
The present invention relates to a track control circuit for an optical card recording/reproducing apparatus and, more particularly, to a track control circuit for an optical card recording/reproducing apparatus for controlling the amplitude of a track error signal from an optical card.
2. Description of the Related Art
A conventional optical information recording medium such as an optical card having a large volume of information has a plurality of tracks in its data recording area at predetermined intervals. In an optical card recording/reproducing apparatus serving as an information recording/reproducing apparatus, a desired track of the optical card is irradiated with a recording/reproducing light beam. A focus servo system is controlled to obtain an in-focus point of the light beam on this track. At the same time, a track servo system is controlled so that the light beam is always located at the center of the track. A focus error signal representing a deviation from the in-focus point and a track error signal representing a positional error from the center of the track are required as signals for controlling the focus servo system and the track servo system.
The light beam is split into a main beam and sub-beams which interpose the main beam therebetween in accordance with a known 3-beam method. These three light beams are detected by a photosensor so that beams the reflected by the optical card are received and the reflected light amounts are detected. Of the detected beams, the main beam is used to obtain the focus error signal, and a difference between the remaining two sub-beams is used as the track error signal.
More specifically, the first and second detection signals representing the reflection light amounts of these two sub-beams are input to a subtracter. A difference between the first and second detection signals is calculated by the subtracter and is output as the track error signal.
The track servo system is arranged as follows. The difference between the first and second detection signals is calculated by the subtracter, and at the same time, a sum of the first and second detection signals is calculated by an adder. An output from the subtracter is divided by an output from the adder by a divider to obtain the track error signal. This divider is used to eliminate influences, on the track error signal, of contamination of the data recording area of the optical card, variations in reflectances of tracks caused by fingerprints of users, and changes in intensities of the light beams in the recording and reproduction modes.
The track error signal output from the divider is input to a track actuator through a switch opened/closed by controlling a track ON signal from a control unit and through a drive amplifier. Therefore, the light beam is adjusted to control tracks.
In general, reflectances of tracks formed in the data recording area of an optical card and guide tracks formed at both sides of the tracks along then considerably vary, and various combinations of reflectances are given. For example, in the track servo system having the arrangement described above, influences, on the track error signal, of contamination and fingerprints o the data recording area of the optical card can be eliminated.
When a difference between reflectances between a track and a track guide is changed, the amplitude of a track error signal is changed. For this reason, the gain of the track control system is changed to result in unstable track control. In such a conventional track servo system, when a difference between reflectances of a track and a guide track of an optical card is large, the light beam must be adjusted depending on the optical card used.